There has been proposed, an automatic driving technique for bulldozers, for example, in Japanese Patent Laid-Open Publication No. 7-26586(1995), according to which a bulldozer is automatically driven by radio control or the like within a specified lane when manual driving by the operator is impossible or too dangerous to carry out during digging/carrying operation.
In such automatic driving, accurate measurements of the vehicle speed (ground speed) and travel direction of the vehicle are necessary to establish the present position of the bulldozer. The following methods for measuring the speed of a track-laying vehicle such as a bulldozer are generally known: (1) Vehicle speed is determined from the rotating speed of the crawler belts, that is, the rotating speed of the sprockets for the crawler belts. (2) Vehicle speed is detected by a Doppler sensor (Doppler vehicle speed). It is generally known that the vehicle speed detection based on the rotating speed of the crawler belt sprockets is more accurate than the detection by a Doppler sensor.
The detection based on the rotating speed of the sprockets, however, presents the disadvantage that the vehicle speed detection cannot be accurately carried out when there occurs a slip (shoe slip) in the crawler belts due to increases in the load on the blade (i.e., actual tractive force).
For accurately determining the travel direction of a vehicle body, it is necessary to clearly distinguish, for example, between when the vehicle travels forward with the crawler belts being not parallel with the ground level and when the vehicle travels forward along a slope.
Accordingly, the present invention is directed to solving the above problems and one of the objects of the invention is therefore to provide a bulldozer location system capable of providing greatly improved accuracy in calculation of a travel distance by obtaining the accurate vehicle speed and travel direction of a bulldozer.